cors and snarf
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CORS and SNARF
Giovanni Sella
NOAA- National Geodetic Survey
giovanni.sella @ noaa.gov
AGU Fall Meeting SNARF Splinter Session
San Francisco, CA
December 11, 2007
CORS Network in CONUS 2007
CORS Monthly Data Downloads 2002-2007
CORS
New sites continue being added rapidly
Monumentation of new sites has improved(MA building 17ft pillars)
All use force centering devices
Monumentation information is stored both photographs and text descriptions in logs (many older sites are still lacking in this info)
Continued revising meta data and now checking all online storage data.
NGS Mission
NGS is responsible for defining, maintaining and providing access to the National Spatial Reference System for the civilian sector of the US government
CORS provide two critical elements to this, direct access to the NSRS which is in large part defined using CORS coordinates and for post-processing positioning services e.g. OPUS and OPUS-RS
Legal binding datum for the United States is NAD83
Evolution of NAD83
NAD83 (1986) relied on Doppler COM, orientation, and scale
COM was off by 2m compared to ITRF and orientation off by 0.03 arc seconds and scale by 0.0871 ppm
NAD83 (HARN) (1989) state-by-state update kept same COM and orientation but adopted ITRF scale (ellipsoidal coordinates changed by -0.6m.
NAD83 (CORS93/CORS94/CORS96) tied to a multi-year analysis of CORS nationwide transformation kept original COM and orientation (from 1986) scale equal to ITRF
Future NAD83 and SNARF
NAD83 is an international effort
NAREF is the vehicle for combining new solutions
After complete re-processing by all participating agencies and new multiyear NAREF solution. Revision of NAD83 considered (~2010?)
SNARF is the scientific frame which can be used as the template for NAD83 revisions
Changes in frame definitions are delicate “business” due to large legal implications
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